Timing or burned valve

[liv2soar]

Earlier I wrote this....<br /><br />My 1986 Bayliner with an AQ-131 4 cylinder inline inboard/outboard isn't running too good.<br /><br />In nuetral it runs great all the way to the redline. <br /><br />When I engage the prop, it starts backfiring a fuel/air spray out of the carburetor. <br /><br />How could the timing be off if when in nuetral it runs perfect all the way to the redline at 4500RPMs?<br /><br />Could this be a burned valve, I did have this problem begin the next trip to the lake after a water pump went out. Could it have overheated it and burned a valve up?<br /><br />And also my only other thought is the vacuum advance, I'm not familiar with it, how do I check to see if my 86' AQ-131 has one or not?

 

[imported_Mike_M2]

Re: Timing or burned valve

Without a load on the engine it will run better. When is the last time the timing belt was changed? If it's been a while, that's the first thing i would check, it could have jumped a tooth. I do not believe there's a vacuum type advance on that motor.

 

[boat doc]

Re: Timing or burned valve

you will have a vacume hose that runs to your distributer if you have vac. advance, do a compresion test for a burned valve. Call me crazy, or I am just not old enough, but I have not seen a timing belt on marine engines.

 

[imported_Mike_M2]

Re: Timing or burned valve

Ain't gonna call you crazy, but yea, the AQ's had belts. I broke one myself one time! The AQ was no more than an old Volvo car 4 cyl. they adapted to marine use...

 

[metwrench]

Re: Timing or burned valve

Thats Wild !! A timing belt in marine Application ?? I have Millions on Autos, But never on a Boat ! Wow....<br /><br />Yes, Compression check will show a Burnt Valve, But that doesn sound like thats the problem to me. Check for the Vac advance to see if it has one. Vac Advance is for FAST / Rapid Acceleration of Timing to go Advanced, Mechanical Advance is slow steady cruise advance of timing. If you suspect " timing" I would throw a Timing light on it in Nuetral, then engage and see if the timing drastically changes ... Also, Does the Motor run Hot at all ? Temp of the engine ?? When you place it engaged and its Sputters, what happens when you try to accelerate ?

 

[vinney]

Re: Timing or burned valve

Thats a common problem for the timing belt on the Volvo Penta AQ125 engine to jump time. The raw water pump leaks and rust the pulleys for the timing belt. Crankshaft,camshaft and aux.shaft for the distributor. Remove the front cover for the timing belt. There are three timing marks on the block and a timing marks on all the pulleys. There is a pulley/adjuster that hold the belt tight that the bearing will fail also. Check you timing first. There is no a vacuum advance on marine engines. This engine is not known for burn't valves.

 

[metwrench]

Re: Timing or burned valve

Thats why Vinney is a Petty Officer First class and I am Just a Seaman Apprentice !! You can tell a Car Mechanic from a marine Mechanic..Thanks Vinney for correcting me on the Vac Advance...I forgot Marine doesnt run that..

 

[liv2soar]

Re: Timing or burned valve

Thanks Vinney,<br /><br />Sounds like you've got some great knowledge on Volvo's. I just gave up with the boat and took it to the local volvo-penta mechanic. He said it's common that when the timing goes out the engine will run rich. All spark plugs were black and sooty looking as if it was running very rich.<br /><br />When in nuetral the engine would vibrate, but still ran ok. The boat is still new to me though. But it sure didn't run as smooth as my automobile engines does.<br /><br />So in your opinion the belt may have skipped a tooth on the wheel and it can be corrected by placing the belt back on and setting the timing huh?<br /><br />Scott A

 

[Dunaruna]

Re: Timing or burned valve

If its stretched enough to jump a tooth it is time for replacement. As vinney said, don't forget the pulleys.<br /><br />Hope this helps - sorry for the poor quality.<br /><br />2.3 (141cid) Litre Volvo Penta timing belt:<br />

<br /> <br /><br />Aldo

 

[vinney]

Re: Timing or burned valve

If your lucky YOU only need a timing belt. Maybe pulleys or adjuster. Hold on Volvo stuff isn't cheap. If the belts correct after you get it back from the shop You will love that engine they run well. You need a new timing belt if its jumped time. I think that diagram stuff is great.